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Transport Membrane Condenser (TMC) is a promising technology that works based on the capillary condensation property of the nano-scale ceramic porous membrane materials and can recover both waste heat and water in various industrial applications. For applications with high volume flow rate such as in power plants, a large number of TMC heat exchangers are required, which highlights the importance of the optimum design for the TMC exchangers in order to obtain the maximum heat transfer and minimum cost of the TMC heat exchanger unit. In this paper, the effects of different tube spacing and the inlet water vapor mass fraction on the overall performance of a membrane-based heat exchanger have been studied numerically using a combined condensation model based on the capillary condensation and condensation on a solid wall. The results were obtained in terms of the Euler number, dimensionless volumetric heat transfer density, and contours of the water mass fraction and temperature distribution inside the TMC heat exchanger. [ABSTRACT FROM AUTHOR]

During gastrointestinal endoscopy, endoscopy is pushed into human digestive tract with the aid of outside force, which may cause a series of complications due to repeatedly inserting, rotating, pushing and retrieving operation. These are serious friction damage problems that few studies have focused on. In this paper, the friction behavior between the front-tip of gastroscopy and esophageal wall tissue during endoscopy was studied by using a UMT-II Micro-Tribometer. Fresh porcine esophagus of different anatomical sites (thoracic, abdominal and cervical esophagus) and layers in vitro was chosen as the tissue samples. The normal force was from 0.2 to 1.0 N, the sliding speed was from 0.1 to 0.9 mm/s, and the unidirectional sliding displacement was 22 mm to simulate the endoscopy manipulation. Results showed that the typical “stick-slip” phenomena appeared in the process of the front-tip sliding on the esophageal internal surface, which was related to the alternating deformation, recovery as well as the energy dissipation of esophageal tissue. The friction coefficient decreased with the increasing normal load and increased with the increasing sliding speed. Since the physiological structure and mechanical property of esophagus were diverse in different anatomical sites and layers, there would be a lower friction coefficient in the thoracic esophagus compared with the cervical and abdominal esophagus. Besides, the friction coefficient in intact esophagus was larger than that in layered esophagus. The results can provide the basic data for safety operation and damage control during gastrointestinal endoscopy. [ABSTRACT FROM AUTHOR]

Abstract: Experimental investigations were conducted to determine the condensation heat transfer and pressure drop of refrigerant R134a in annular helicoidal pipe at three inclination angles. The experiments were performed with the Reynolds number of R134a ranging from 60 to 200, and that of cooling water from 3600 to 22000; temperatures of R134a at 30°C and 35°C, and cooling water at 16°C, 20°C and 24°C. The experimental results indicated that the refrigerant Nusselt number was larger at lower refrigerant saturation temperature, and would increase with the increase of mass flow rates of refrigerant and cooling water. It was found that the refrigerant heat transfer coefficient of annular helicoidal pipe could be two times larger than that of equivalent plain straight pipe when the refrigerant Reynolds number was larger than 140. Comparison with identical helicoidal pipe with opposite flow channel arrangement revealed that the refrigerant heat transfer rate was larger when the refrigerant was flowing in the annular section at the cooling water Reynolds number larger than 4000, but the pressure drop was always larger in this flow channel arrangement. [Copyright &y& Elsevier]

Abstract: A two-dimensional single phase computational fluid dynamics (CFD) model of microbubble-laden flow over a flat plate was used to assess the role of mixture density variation in microbubble drag reduction. The model consisted of Reynolds-averaged Navier–Stokes (RANS) transport equations, a standard k–ω turbulence model, and a convection–diffusion species transport model. Performance of the model was validated with available experimental data and numerical simulations of more advanced multiphase two-fluid model. A parametric study of the density ratio effect on the drag reduction was carried out. The study indicated that simple mixture density variation effect plays one of the major roles in the microbubble drag reduction phenomenon. Also, the influence of the density ratio (the ratio of density of injected gas to that of water) on gas volume fraction profiles was found to be minimal within studied parameter range. [Copyright &y& Elsevier]

Abstract: The decontamination and decommissioning of radioactively contaminated structures and facilities, volume reduction of massive metal structures, and demolition of large concrete structures, result in release of large quantities of contaminants that become airborne and thus could be inhaled by workers and population living in the neighborhood. In order to provide adequate protection to the workers, adequate monitoring of the airborne particulates and proper models that predict the dispersion of the airborne contaminants are needed. The dispersion model will enable development of decision tools on the extent of decontamination that needs to be performed prior to dismantlement and the optimization of personal protective equipment requirements during D&D operations. The Gaussian plume dispersion model is used in this study to predict the dispersion of airborne particulate PM10 (d p <10μm) released from: (1) a 35m height contaminant plant where the plume is affected by the presence of 36 buildings around the emission source, (2) a building during decontamination and removal of process equipment and (3) demolition of contaminant building. The potential impact of PM10 on 180 receptors located at five downwind distances between 0.1 and 20km around the emission source was performed. A short-term (1–48h) prediction of average concentration of PM10 from point and area sources on receptors located at ground level was obtained. The concentrations of PM10 over 24h time period were compared to the U.S. air quality standards. The results obtained in the course of this study are used to predict the inhalation exposures of workers and population living in neighborhood. [Copyright &y& Elsevier]

Abstract: Condensation heat transfer and pressure drop data of R-134a in annular helical pipes is of significant importance to the effective design and reliable operation of helical pipe heat exchangers for refrigeration, air-conditioning, and many other applications. This paper presents the experimental investigation on condensation heat transfer and pressure drop characteristics of R-134a in an annular helical pipe. The average condensation heat transfer coefficients and pressure drops were experimentally determined for R-134a at three different saturated temperatures (35 °C, 40 °C, and 46 °C). The experimental results are compared with the data available in the literature for helical and straight pipes. [Copyright &y& Elsevier]

Abstract: Demand for greater engine efficiency and thrust-to-weight ratio has driven the production of aircraft engines with higher core temperatures and pressures. Such engines operate at higher fuel–air ratios, resulting in the potential for significant heat release and chemical reactions on a film-cooled surface. Currently, there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. In this paper, the chemically reactive turbulent film cooling over a surface for three cases of an inclined single and two parallel and compound-angle coolant holes is investigated by a Reynolds-averaged Navier–Stokes approach with the shear-stress transport (SST) turbulence model using OpenFoam. To take into account the secondary combustion resulting from the unburned fuels in the crossflow, a two-step reaction scheme was used for the combustion of propane. The relative increase in surface heat flux due to near wall reactions was investigated for film cooling with N2 and air injections. An eddy dissipation concept fast chemistry approach was used to account for the turbulence–chemistry interaction. Results demonstrate that reactions in the turbine cooling film can result in increased heat transferred to the surface. Failure to design for this effect could result in augmented heat transfer caused by the cooling scheme, and turbine life could be degraded substantially. The analysis suggests that high fuel–air ratio designs may have to consider changes to cooling strategies to accommodate secondary combustion. [Copyright &y& Elsevier]

Abstract: Non-premixed turbulent reacting flow in a methane-fuelled coaxial jet combustor has been studied numerically employing Reynolds Averaged Navier–Stokes (RANS) models. A local extinction approach for treating chemical reaction kinetics within the eddy dissipation concept (EDC) has been examined. It applies a database of pre-calculated chemical time scales, which contains the influence of chemical kinetics that is otherwise time-consuming to calculate. Simulations were carried out using standard k-epsilon, RNG k-epsilon and k-Omega SST turbulence models by open-source CFD-toolbox OpenFOAM. The results were compared to available numerical results and experimental data for predicting velocity, and temperature fields. All simulations were conducted with a reasonable number of meshes to demonstrate the accuracy of different turbulent RANS models in OpenFOAM solver which has a wide range of engineering applications in such type of flows. [Copyright &y& Elsevier]

Abstract: The structures and damping characteristics of the NiTi shape memory alloy using different heat treatment methods have been clarified by X-ray diffraction, differential scanning calorimetry, and damping analysis. Especially, we studied the dependence of damping characteristics on temperature, and the relations between vibration frequency and the transformation of the material. The results show that the structure of the alloy with slow cooling consists of large amounts of the M and R phases, and the Ni-richer Ti3Ni4, so that the damping level of the alloy is higher and produce a low frequency damping peak in the temperature area corresponding to the M→R reverse transformation in the reheating process. It is of technological importance. [Copyright &y& Elsevier]

This experimental study focused mainly on the solidification of a binary mixture of ammonium chloride and water (NH4Cl–H2O) in a differentially heated cavity. One vertical wall was cooled to temperature TC=−20 °C, and the other opposite vertical wall was kept at a constant temperature TH=+20 °C. The effect of the initial concentration of ammonium chloride on the solidification process was considered. Particle image velocimetry was used in this study for the visualization of the dynamic field during the solidification process. The temperature distribution at discrete locations in the solution and on the vertical cooling wall were monitored using thermocouples. The convection flow patterns, the ice thickness, and the temperature distribution were obtained for various initial concentrations of ammonium chloride ranging from 0 to 20 wt.% (sub-eutectic and near-eutectic growth). The results obtained in the course of this study reveal that (1) the initial concentration plays a significant role in the evolution of convection flow patterns, (2) the thickness of the frozen layer depends on position inside the cavity (top, middle, bottom), (3) the ice growth rate was almost double at the bottom of the cavity, and (4) the process of solidification is slower with an increase in the initial concentration levels of the binary solution. [Copyright &y& Elsevier]

Three-dimensional laser Doppler anemometry measurements are performed on developed laminar flow in three helical pipes. The experimental observations are compared to results of numerical calculations employing the fully elliptic numerical method. Good agreement is found between measured data and numerical results. The three helical pipes, with curvature ratios of 0.0734 and 0.1374 and non-dimensional pitches of 0.0793 and 0.193, are adopted to study the effects of curvature and pitch on laminar flow in the experimental approach. The range of Reynolds numbers is 500–2000 to ensure laminar flow in the entire helical pipe. Both the profile shapes of the normal components of the secondary flow and those of the axial flow along the same centerline present not only similar patterns but also similar change when pitch, curvature ratio, and Reynolds number vary. The results demonstrate comprehensive relationships between the axial flow and the secondary flow. [Copyright &y& Elsevier]

In this paper, a simplified 3D algebraic slip mixture (ASM) model is introduced to obtain the numerical solution in sand–water slurry flow. In order for the study to obtain the precise numerical solution in fully developed turbulent flow, the RNG K–&epsiv; turbulent model was used with the ASM model. An unstructured (block-structured) non-uniform grid was chosen to discretize the entire computational domain, and a control volume finite difference method was used to solve the governing equations. The mean pressure gradients from the numerical solutions were compared with the authors’ experimental data and that in the open literature. The solutions were found to be in good agreement when the slurry mean velocity is higher than the corresponding critical deposition velocity. Moreover, the numerical investigations have displayed some important slurry flow characteristics, such as volume fraction distributions, slurry density, slip velocity magnitude, slurry mean velocity distributions, and slurry mean skin friction coefficient distributions in a fully developed section, that have never been displayed in the experiments. [Copyright &y& Elsevier]

In this study deformation of a falling drop which is surrounded by another liquid is modeled analytically and numerically. The drop is influenced by an external electric field which is applied uniformly on the side walls of the domain. An open-source volume-of-fluid solver, Gerris with dynamic adaptive grid refinement has been used for numerically modeling the three-dimensional deformation of a falling droplet. Analytical solutions of drop's deformation are presented in detail and then the outcomes are compared with numerical results. The numerical results are presented for various values of density ratios and electrical conductivity and permittivity. The comparison of the results shows a great agreement between the analytical solutions and the direct numerical simulation (DNS) results. [ABSTRACT FROM AUTHOR]

Physical properties and especially the size of drops are important parameters in many industrial and medical applications. High voltage electric field is one of the effective means to control the final size of drops during the fabrication process which could greatly influence the final size of the product. Therefore a detailed study of electric field effect on a liquid drop is very important. In this work deformation and fragmentation of a falling droplet under gravity and electric force have been studied numerically. Electric force is used as an effective external controlling mechanism to influence the deformation of a drop. The three-dimensional deformation of a falling droplet is studied numerically using the open-source volume-of-fluid solver, Gerris. The numerical results are compared with previous analytical, experimental and numerical data and great agreements between the results are obtained. The results are presented for broad range of Bond numbers ( Bo ) from low Bond number (drop with small deformation) to large Bond number (drop breakup and fragmentation). The results revealed that the electric field can be used as a powerful controlling tool in delaying and expediting the falling drop breakup process. The results also showed that falling drop deforms severely by increasing Bo number which leads to the breakup and fragmentation compared to the cases of low Bo number in which the drop deforms mildly without breakup. [ABSTRACT FROM AUTHOR]

Exfoliated layered double hydroxide (LDH) nanosheets are a class of positively charged 2D nanoparticles. These LDH nanosheets can be used for a wide range of functional polymer nanocomposites and hierarchically structured materials. In this review we summarize and evaluate latest scientific advances in exfoliating LDH compounds, including exfoliation methods, mechanisms, properties and applications of exfoliated LDH nanosheets. Then identify the prevailing challenges and the directions of future work. In the first section of this review we dicuss the liquid exfoliation of LDH compounds, free of intercalation of organic species, in formamide, saturated aqueous L-asparagine or aqueous NaOH/urea solution with the help of ultrasonic treatment, mechanical shaking or stirring. We then examine the liquid exfoliation of LDH compounds with preceding organic species-intercalation. Such organic species include carboxylate, sulfonate, dodecyl sulfate, and amphoteric biomolecular amino acids. Next, we dicuss the exfoliation of LDH in monomer or polymer to form LDH/polymer nanocomposites. The polymer nanocomposites include LDH/polyethylene, LDH/polyethylene- graft -maleic anhydride, LDH/poly (vinyl alcohol), LDH/polystyrene, LDH/poly (ethylene terephthalate), LDH/poly (butylene adipate- co -terephtalate), LDH/poly ((butylene succinate)- co -adipate), LDH/poly caprolactone, LDH/poly ( l -lactic) acid, LDH/acrylic polymer, LDH/polyacrylamide, LDH/poly(amide-imide) and LDH/poly (methyl methacrylate). The properties of these LDH/polymer nanocomposites are also discussed. In addition to polymer nanocomposites, recent studies indicate that the exfoliated LDH nanosheets can be used in electrorheological media, magnetic materials, low infrared emissivity materials, catalysts, and biosensors. The literature survey and analysis suggests that future work should place emphasis on the innovation of green and cost-effective exfoliation methods, and deepen understanding of the interfacial interactions between the LDH nanosheets and organic species/polymers, and the new assembly tactics of exfoliated LDH nanosheets with functional molecules or nanomaterials to expand applications. [ABSTRACT FROM AUTHOR]

Abstract: In this work, sugar-derived carbon microspheres (CMSs) with diameters in the range of 5–10μm and uniform nanopores were prepared using the subcritical water carbonization method, followed by microwave-assisted KOH activation. The carbonization was conducted at 3MPa and moderate temperatures (150–170°C) in subcritical water, which is a green dehydrating agent. The formation of the CMSs from a sugar solution under subcritical water conditions followed a radical-catalysed emulsion polymerization mechanism. The specific surface area and pore volume of the CMSs were found to increase with increasing the mass ratio of KOH over carbon up to 1:1. Electrocapacitive results showed that a sample prepared at a KOH to carbon ratio of 1:1 and microwave irradiation level of 70% possessed the highest specific capacitance (about 179.2F/g) at a current density of 1A/g and excellent cycling performance over 1000 charging/discharging cycles without significantly loss in capacitance. The specific capacitance and capacitive retention of this electrode are comparable to that of an electrode prepared from commercial YP-80F activated carbon. [Copyright &y& Elsevier]

Abstract: Catalyst-free transesterification of leather tanning waste with high free fatty acid (FFA) content at supercritical condition was reported in this work. The experiments were performed in batch system at various temperatures (250–325°C) under constant pressure of 12MPa and methanol/fatty oil molar ratio of 40:1 for reaction time of 2–10min. Kinetic modeling of formation of fatty acid methyl esters (FAMEs) that incorporate reversible esterification and non-reversible transesterification simultaneously was verified. The proposed semi-empirical model was fitted against kinetic experimental data over temperature range studied. The kinetic parameters (i.e. k′TE, k′E, and k E′) were determined by nonlinear regression fitting. Thermodynamic activation parameters of the reactions were evaluated based on activation complex theory (ACT) and the following results are obtained: ΔG ‡ >0, ΔH ‡ >0, and ΔS ‡ <0. The activation energy (E a ) of transesterification, forward and reverse esterification reactions was 36.01kJ/mol, 28.38kJ/mol, and 5.66kJ/mol, respectively. [Copyright &y& Elsevier]

Abstract: A facile and green preparation of high surface area activated carbons with mixed microporosity and mesoporosity from durian shell waste is reported in this work. The pore structure and surface chemistry of the parent carbon were modified by the combination of ultrasonication and microwave irradiation techniques. The effects of temperature and time in the ultrasonication treatment and power output and time in the microwave irradiation were studied. The electrochemical performance of carbon electrodes for supercapacitors was tested by cyclic voltammeter (CV) and galvanostatic charge–discharge. The results show that the capacitive energy storage of electrodes is critically dependent on the microporosity and surface chemistry of activated carbons. The highest electrode capacitance in this work was 103.6F/g that prepared from activated carbon modified at an ultrasonication temperature of 323.15K for 10min and microwave power output of 900W for 10min. [Copyright &y& Elsevier]